When a typical internal combustion engine is used in a boat, engine coolant flows in a closed loop through the engine block and a heat exchanger which transfers the waste engine heat to the water body in which the boat floats.
Typically, elevated temperature exhaust gas from each engine combustion chamber is collected by an exhaust manifold which is affixed to the engine block, so the gases can flow down an exhaust pipe which penetrates the boat hull. The exhaust pipe typically has a water jacket, through which is flowed the engine coolant. The purpose of such is to limit heat loss from the exhaust pipe, so that things or persons in the boat might not be harmed by contact with the hot pipe, and to limit heating of the boat interior. In engines expressly made for marine use, the exhaust manifold is typically water cooled, for the same reason the exhaust pipe is cooled. Typically, a cooled exhaust manifold is a casting or weldment that has hollow walls, to form an integral water jacket within which coolant water circulates. Such manifolds work well, but of course are substantially more costly to make than uncooled manifolds.
Industrial engines (those designed for uses other than marine) typically have uncooled exhaust manifolds. But because of the wider diversity and availability of industrial engines, it is often desirable to adapt them to boat use. However, in doing that the heat loss from the manifold can be a problem. In addition to the reasons just given, further heat-related difficulties can arise when the engine is contained within a sound insulating enclosure. The enclosure tends to prevent convection and radiation which otherwise occur. Thus, the temperature within a sound shield enclosure can rise to the point of deteriorating the sound insulating materials, or organic components near the engine.
However, even ignoring cost considerations, a water cooled manifold cannot be conveniently installed in replacement of the uncooled manifold on an industrial engine, to adapt it for marine use, even though from an engineering and engine performance standpoint, that would be fine. The reason is that current environmental regulations of the United States and other countries, relating to gaseous emissions of internal combustion engines, require testing and certification of internal combustion engines, including those used in land vehicles, stationary applications, and marine vessels. Once certified, changes in the design of any component, from the intake inlet to exhaust outlet port—thus including the exhaust manifold, cannot be made without securing further regulatory approval. So, if an industrial engine is certified for its land-based use with an uncooled manifold, it cannot be re-fitted with a cooled manifold and installed in a boat, unless the engine is re-certified. Recertification can be costly and time consuming. The apparent basis for the recertification requirement is that the cooler running manifold can effect engine emissions. Thus, the use of industrial engines in boats is inhibited, in large part because it is often not economically feasible for makers of land-use engines to have them re-certified for marine use, if the expected volume is low, as it often will be.
There is thus a need for a way to install industrial engines in boats while minimizing heat loss from the exhaust manifold, without the high cost of re-certification to meet environmental regulations.